Why cant i protect myself from everything?

Hey, howcome my body cant defend itself from aids, and cancer? I know that we cant defend our bodies against aids because aids changes its shape so our white cells cant latch on and do their job, but howcome our body can do such complex tasks, yet it cannot figure out its pattern??

Other things like cancer, is this the same reason why our antibodies cant fight the virus?

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another_someone

The problem with HIV (AIDS is the collection of symptoms - the virus is HIV - old politics) is not so much that the virus changes shape (this is a wider problem with vaccines, but is not the biggest problem the body faces), but that the T cells which are sent to attack the virus actually become infected by the virus, and so it attacks the very functions that try and protect you from it.

Cancer, like AIDS, is a symptom, but it has a wide variety of causes.

The problem with protecting yourself against everything is that protecting your body against disease is like protecting your house against burglary - you can protect yourself against most people breaking into your house, but no matter how clever you get in installing defences against a burglar, there will always be at least one burglar who can find a way around those defences.

There is another problem that is similar between protecting against burgary and protecting against disease - they both carry a cost. You can improve your defences against a burglar by surrounding your house with high walls, lots of locked gates, lots of security guards and cameras, etc. - but all of this costs money, and in other ways makes like less convenient (you can't go home without disabling a burglar alarm, friends cant just casually drop in and visit without passing through security, and you can't just ask your neighbour to drop in feed the cat while you are away).

The same is true when you develop sophisticated defences against disease - there are biological costs to those defences, so the body implements only as many as it thinks are normally necessary (bearing in mind that the human body is only designed for a limited lifespan anyway, so having a body that defends against disease for 200 years when it will anyway probably die in 90 years becomes an unnecessary burden).

The other issue is that often a defence against one disease becomes a weakness for another disease. In the case of HIV, it is the very T cells that are part of the system for fighting disease that become the entry point for the viral attack.